Abstract Assignments of ν(SiH) and ν(SiD) modes in SiHX 3 , SiH 2 X 2 and SiH 3 X compounds are surveyed. With a few exceptions, ν(SiH)/ν(SiD) ratios are found to be those expected on the basis of harmonic local mode calculations, if ν(SiD) values are first divided by a factor R which normally lies in the range 1.010–1.011. Major deviations from this range indicate misassignments or Fermi resonances. Stretch-stretch interaction constants f ′ a are tabulated, and agree excellently with ab initio values, where these are available. Where ν is (SiH) values are known, the frequency sum rule is found to be obeyed closely. The ν 7 bands of Si 2 H 6 and Si 2 D 6 are reanalysed to yield an R value of 1.010. The ν(SiH) data for disilanes then yield, in a “6 × 6” refinement, values of the three interaction force constants f ′ a , f ′ g and f ′ g , together with predictions of hitherto unlocated stretching fundamentals. Constancy of the R factor for different types of XH bonds is shown to be a consequence of Dennison's rules, and similar anharmonicity factors.